Communicating with other resource groups when behind a firewall

Hi!

I have a vm located in North Europe on resource group A. 

On this server I have a webservice that is protected by a firewall allowing only a few select IP addresses to connect.

On resource group B in North Europe I have a storage account and a function that triggers when that is updated. 

I want to send updates with that function on resource group B to the webservice on resource group A but I do not want to open up the firewall for all IP addresses on the North Europe data center.  

Any thoughts on how to achieve this? 

Best regards,
Mattias